Blender's DrawKeyframe feature works great for object animation. I would like to propose a couple of additional features that would improve Armature animation as well.
As you all know, when this feature is activated the object keyframes are drawn as "yellowish ghosts" in the 3D window.
If the object is an armature, and it has an action, the "ghost armatures" keep being animated together with it when the frame changes.
So, the idea is that these "ghosts" get pinned in the pose corresponding to the frame they represent instead of the current behaviour.
Then we could just click on the "ghost" to change the particular pose (pose mode) or move the character (object mode).
Moreover, "Onion skinning" feature is very close to this. The only thing missing is ability to draw extra "ghosts" before and after the selected keyframe.
I'll second that, again. At least the onion skinning feature has been requested multiple times before. I guess we'll see it some day =) Personally I'd be more happy about something that would show me the 'arcs' in my animation. There is a script (found on elysiun) which works very well - but once again, only for objects, not armatures. These are heavily used features in other packages, because they are so increadibly useful. I guess we have to learn a bit more C =). Or hope the Orange project will require this.
I agree with malefico. This would be an useful feature for a better workflow. We could see the arcs, and apply the secondary animation easily.